1. Field of the Invention
The brace of the present invention reinforces the structural members of an offset truss used to span spaced apart building walls. An offset truss is one where the structural components of the truss are not in a single plane and is defined as one made by nailing the roof rafter against the side of a ceiling or cross tie joist at the position where the joist rests on the top plate of a building wall.
In the past a lumber plank of generally 1" nominal thickness by 5" or 6" wide has been used to brace these diverging joists and rafters. The wooden plank brace would be disposed intermediate the heel joint of the truss and the ridge board of the building roof. Because of the offset arrangement of the joist and rafter the wood plank had to flex the amount of its thickness--usually in a span of 30" or less. This flexing necessity required the use of quality lumber or the plank would crack at the time of flexing. Obtaining consistently quality lumber is becoming more difficult and when it is obtained the price is very high. The use of metal substitutes for wood has existed for many years. Steel in particular, because of its strength has been used in building structures. Some have used steel entirely and others have used a combination of steel and wood. The present invention concerns the use of a steel brace for basically wood frame members. Because of the thinness of the steel used the problem of flexing is eliminated. It is a requirement that the steel brace which replaces the wood plank be as strong in every respect as the wood it replaces. The inherent tensile strength of the steel easily matches the tensile strength of the wood and with the steel brace ribbed as set forth in this invention it fully matches the strength of the wood in its compression loading. It is the particular ribbing arrangement throughout the length of the steel braces in combination with the provision for flat nailing surfaces at each opposite end of the braces that comprise applicant's inventive concept.
2. Description of the Prior Art
A search has disclosed the following prior patents which appear to have pertinence relative to the present invention.
U.S. Pat. No.--Tudor 811,003--Jan. 30, 1906 PA1 British Pat. No.--Junkers 340,412--Jan. 1, 1931 PA1 British Pat. No.--Gibbs 534,267--Mar. 3, 1941 PA1 "As regards the buckling stresses it has been found that rods of this kind when subjected to compression in a network yield first of all at the point where the web portion converges into the flat end portion." PA1 "According to the invention, the desired increase in resistance to buckling is obtained by providing the web, which is otherwise flat, with auxiliary embossments, corrugations or other shapes having a stiffening effect, in the vicinity of the ends of the bar only, such additional stiffening shapes extending approximately in the axial direction of the bar as far as the boundary between the web and the end portion, but not into the latter, so that, as in the embodiments already known, the whole of the end portion of the bar can remain flat." PA1 "In order to strengthen the vertical and diagonal members these latter are provided with channels 6 (see FIG. 3), which are formed by indenting the metal by a rolling or pressing operation. Such channels 6 give rigidity to a strip which would otherwise be flexible, and extend almost to the ends of the members 5 and 6, leaving a short portion flat where these members are attached to the sides of the top and bottom members 1 and 2."
The 1906 Tudor United States patent shows a metal brace having a longitudinal rib throughout its major extent, but leaving plain flat marginal ends to enable the brace to flatly abut a surface in use.
The 1931 British patent to Junkers describes a bar or brace fabricated from sheet metal. It is reinforced to withstand buckling from compression loads by bent side flanges as well as ribs impressed in the brace adjacent its flat ends. This British patent recognizes the culpability of the brace to buckling when subjected to compression loads. On page 1, lines 41 to 46 of the Junkers patent, the specification read as follows:
And, on page 1, lines 53 to 66 this British patent reads as follows:
In this British patent to Junkers it is evident the ribs and flanges stop short of the ends of the brace to permit its attachment in application. It is probably true that the closeness of the special stiffening ribs to the flat ends will likely minimize buckling under compression. However, buckling is not eliminated because the ribs do not extend into and through the attaching end portions.
The 1941 British patent to Gibbs discloses bracing formed with side flanges and ribs for strengthening. On page 1, lines 86 to 96 of the Gibbs patent, the specification states:
Here again the ribs are shortened to leave flat ends for attaching the brace in use and it is vulnerable to buckling at those flat end portions.
In contrast to the known prior art applicant's brace is ribbed all the way to the ends and yet provides flat attaching ends on opposite sides for application to offset trusses.